Perspectives

(092112)

Embryos
Tell a Different Story — Often Not Mentioned by Science

Questions:

What
is the idea behind saying that "ontogeny recapitulates phylogeny"?

Does "ontogeny
recapitulate phylogeny" ... does it really? Or is this simply
a misguided slogan? [And if misleading, why is this
concept still taught to biology students?]

What
examples are there where evidence from embryology counters this popular conception
of evolution?

Short Answer:

This
feature article really needs a plain language 'short answer' because it gets
into a technical topic. So take note, as elsewhere within the WindowView, we
are taking a first glimpse at a topic that has broader implications. Consider
this short answer a starting point and that a problem uncovered here cuts through
long-standing assumptions. Additional explorations help to reveal how this further
supports themes presented in other feature articles within the WindowView.

Does "ontogeny recapitulate phylogeny"
... does it really?

The concept that embryology
can illustrate an evolutionary history in the developing stages of many (vertebrate)
embryos is not new. We are told human embryos recapitulate or follow the
stages of development in a sequence covering all the evolutionary steps of
animals preceding our species. A dictionary definition directly reflects this
notion [recapitulate: "Biology.
To appear to repeat (the evolutionary stages of the species) during the embryonic
development of the individual organism." American Heritage Dictionary,
1994]. So, for decades, biology instructors and professors have been
telling students: "ontogeny recapitulates phylogeny." [ontogeny: origin and development of an individual organism from
embryo to adult; and phylogeny: evolutionary
development and history of a species or higher taxonomic grouping of organisms]

The short answer is: This concept seems logical but it is incorrect. The 'logical part' goes to the credit of assumption. A closer
look at embryos of a number of organisms and the illustrations used to promote
the concept fail the slogan that's been taught for so many decades. We'll
not delve into every detail, but references given below lead to detailed descriptions
of why and how this all came about. Without this slogan, one of evolution's
supporting icons or cornerstones is removed.

Our main purpose in
visiting embryology is to expand the view to yet another area where a closer
examination is warranted. If assumptions are unsupported, then it's time to
recognize new questions that surface ... especially as errant concepts are
eliminated.

Consider This:

This story really starts with
comparative embryology. And Charles Darwin is at least one source behind the
slogan that 'ontogeny recapitulates phylogeny.' Let's take a look at how that
happened:

Darwin
considered some of the best evidence for his theory to be the striking
resemblance of vertebrate embryos at an early stage of their development.
He wrote ... "the embryos of mammals, birds, fishes, and reptiles"
are "closely similar, but become, when fully developed, widely dissimilar."
He argued that the past explanation for their embryonic similarity
was that such animals "are the modified descendants of some ancient progenitor." According to Darwin, "the
embryonic or larval stages show us, more or less completely, the condition
of the progenitor of the whole group in
its adult state" (Darwin 1936, 338, 345).

Darwin believed
that evolutionary changes tend to occur in the later stages of development and are gradually pushed back into embryogenesis, with the result that the embryonic development bears the imprint of past evolution (in Ernst Heackel's words, "ontogeny recapitulates phylogeny"). The doctrine of recapitulation fits so nicely with Darwin's theory that it has endured to the present and can be found in many modern biology textbooks. But it was clear to embryologists
even during Darwin's lifetime that it did not fit the facts. Nineteenth-century embryologist Karl Ernst von Baer pointed out that although vertebrate embryos resemble each other at one point in their development, they never resemble the adult of any species, present or past. The most that can be said is that embryos in the same major group (such as the vertebrates, which include fishes, reptiles, birds and mammals) tend to resemble each other at a certain stage before they develop the distinguishing characteristics of their class, genus and species
(Gould 1977; Hall 1992; Raff 1996). Wells (MC) Page 58

The following diagram
is found in a 1924 edition of a biology textbook. This is the widely published
Haeckel illustration that appears to align embryos at parallel points in a
particular species embryological development with other similar, parallel,
stages in other vertebrate species. What would you think of evolution theory
if this illustration were to amount to a slight of hand ... like pulling a
rabbit out of a hat? If illusory, then at the very least we'd ask for a more
objective assessment. What does the embryological evidence tell us when taken
at face value, without assumption, and without any preconceived notion of
how evolution might be revealed?

The diagram above incorporates
images that are made to look more alike than biological reality. For this,
Haeckel and his illustration received criticisms during his professional career.
There are various aspects to the misrepresentation he has assembled. For example,
half of the embryos illustrated are mammals from one order, yet other distinct
vertebrate orders are clearly omitted. Might we say Haeckel dealt from
a stacked deck?

Again, there is something
of a debate that whirls about this diagram and evidence or views that both
support and undercut the validity of the concept built into the illustration.
A considerate treatment of this topic appears in Dr. Wells' book Icons
of Evolution (< bookstore
link). To read this account in its entirety adds both context and sufficient
detail to reveal the serious nature of the issues raised to our attention
here. And be aware, the focus is on embryology that in a most objective
sense is now revealing scientific evidence that is powerful enough to correct
misguided assumptions concerning Darwin's theory. And if embryology tends
to indicate we are not descended from a common ancestor, then let future research
investigate where that leads us!

Look at what Darwin
did with this type of 'evidence,' and see where it ends up. The initial idea
is ...

...
similarities in early embryos not only demonstrate that they are descended
from a common ancestor, but also reveal what that ancestor looked
like. Darwin considered this "by far the strongest single class
of facts in favor of" his theory. Wells
(IC) Page 81-82.(See reference palette
listing of sources)

Haeckel's embryos
seem to provide such powerful evidence for Darwin's theory that some
version of them can be found in almost every modern textbook dealing
with evolution. Yet biologists have known for over a century that
Haeckel faked his drawings; vertebrate embryos never look as
similar as he made them out to be. Furthermore, the stage Haeckel labeled the "first" is actually midway through development;
the similarities he exaggerated are preceded by striking differences
in earlier stages of development. Although you might never know it
from reading biology textbooks, Darwin's "strongest single class
of facts" is a classic example of how evidence can be twisted
to fit a theory. Wells (IC) Page 82-83.

Whether
or not Haeckel was guilty of fraud—that is, deliberate deception—there
is no doubt that his drawings misrepresent vertebrate embryos. First,
he chose only those embryos that came closest to fitting his theory.
... Wells (IC) Page 91

One more comment on
Dr. Wells' book on icons. In his Chapter 5 (Haeckel's Embryos) you'll not
only find the critical points noted here, but also a more even handed and
broader treatment of the topic. For example, in place of the diagram above,
Dr. Wells includes another diagram to illustrate what the real "first"
stage looks like. This revels a more diverse array of forms in place of Haeckel's
set of rather similar looking embryos. Furthermore, Dr. Wells adds a diagram
that goes from fertilized egg to adult organism. Four stages in-between reveal
markedly different developmental sequences. Finally, Dr. Wells illustrates
what he calls the developmental hourglass and in the discussion notes how
"one would presumably conclude that the various classes of vertebrates
are not descended from a common ancestor, but had separate origins."
(Wells (IC) Page 101).

Embryology
starts with studies from the unfertilized egg cell all the way to the full
development of the adult form of each species. It's time to remember to include
the beginning of the story as well as the stages down the line ...

Something
to
keep
in
mind ...

As you read here, keep in mind that there are other interesting
problems that arise from a closer look at data from embryology.
Although not examined on this web page, recent symposia and related
publications challenge the concept that random genetic mutations
occurring during early embryo development lead to evolutionary
innovations. While some scientists say this must be the case, the intricate nature of an embryo's early development illustrates
how random mutations end up with lethal results. So where is the
advancement in evolution? Further discussion of this aspect of
embryology will be addressed in another feature article [A
link will be added here in the future] based on comments
made by Drs. Meyer and Nelson at the Yale
Symposium held November 2000.

Why Not Start
With A Look Earlier In The Embryological Sequence?

How often are we given
a description of the evolution of species from a starting point long after
life's origin. As we've already noted in the Science Area narrative, starting
at the beginning—before life's appearance on earth—creates all kinds
of problems for evolution theory. In fact, it's difficult to conceive of biological
evolution even 'getting off the ground.' So, often the story starts with life as a given. Well, a similar problem in building an objective viewpoint
exists for the world of embryology. If we look at the evidence from embryology
we don't get the smooth transition into evolution's assumed mainstream. The
idea of recapitulation jumps past an entire field of evidence:

Darwin and
his followers ignored these difficulties, however, and the modern synthesis
excluded embryology entirely. Only in the past twenty years, with the
rise of developmental genetics, has comparative embryology attracted
significant interest from evolutionary biologists. One result of this
renewed interest has been the recognition that patterns of early development
of do not fit the Procrustean bed of recapitulationism. Wells (MC) Page 58

We've noted previously
that advances in science fill in gaps from Darwin's day. Again, as stated
in another article within
WindowView, were Charles Darwin alive to consider present day evidence, his
perspectives and theory would differ. He might be the first to set aside much
of what he assumed previously. Microscopy and genetics were advanced much
further in the century to follow Darwin's theory. The evidence of today is
clearly graphic to the extent of drawing very different conclusions ... in
spite of the illustrations and apparent similarities.

After fertilization,
animal embryos first undergo a process called cleavage, ...

Each major group of animals follows
a distinctive cleavage pattern; among vertebrates, for example, mammals,
birds, fishes and reptiles cleave very differently.

Animal embryos then enter the gastrulation
stage, during which their cells move relative to each other, rearranging
themselves to generate basic tissue types and establish the general
layout of the animal's body.

Like cleavage patterns, gastrulation
patterns vary markedly among the major groups of animals, including
the different classes of vertebrates (Elinson 1987).

Only after gastrulation do the embryos
of mammals, birds, fishes and reptiles begin to resemble each other.

Let's review a moment
by being admittedly simplistic. If a logical sequence of developments were
to describe evolution's course through time, then the embryos of each type
of organism—from each new phyla that appeared over time—would come
from some unifying characteristics. The patterns in embryo development would
serve like a trail of crumbs. Follow the trail back and you get to the earlier
and logical ancestral organisms ... and thus the earlier phyla that appeared
on earth.

For example, the way
an egg cell starts to divide shortly after being fertilized might change somewhat
over time as more complex phyla arise, but something in all the patterns of
the way all embryos develop would still serve as evidence for evolution's
trail. So, is the trail there to be found by scientists? As cells divide,
some will eventually turn into key parts of the organism, such as a fore or
hind limb. In the different phyla, from the earlier to latter appearing groups,
one might expect forelimbs to be homologous structures. That is, their embryological
origin ought to be from the same source within the developmental sequence.
But is that true?

Homologous structures are often specified
by non-homologous genetic systems and the concept of homology can seldom
be extended back into embryology. The failure to find a genetic and
embryological basis for homology was discussed by Sir Gavin de Beer,
British embryologist and past Director of the British Museum of Natural
History, in a succinct monograph Homology, an Unresolved Problem.

In some ways the
egg cell, blastula and gastrula stages in the different vertebrate
classes are so dissimilar that, were it not for the close resemblance
in the basic body plan of all adult vertebrates, it seems unlikely
that they would have been classed as belonging to the same phylum.
There is no question that because of the great dissimilarity of the
early stages of embryogenesis in the different vertebrate classes,
organs and structures considered homologous in adult vertebrates cannot
be traced back to homologous cells or regions in the earliest stages
of embryogenesis. In other words, homologous structures are arrived
at by different routes. Denton (ETC) Page 145

Well then, can we at
least say in some way genetic information reveals a common root for homologous
structures? Perhaps the source information holds to some unity while the developmental
paths to get to the structures has simply changed.

The evolutionary
basis of homology is perhaps even more severely damaged by the discovery
that apparently homologous structures are specified in quite different
genes in different species. The effects of genes on development are
often surprisingly diverse. Denton
(ETC) Page 149

Levels of complexity
within biological beings seem to wave a big flag and say 'Evolution isn't
a simple one gene one result process.' Embryology presents a matrix of genetic
and structural relationships. How can one little adjustment in the matrix
of related genetic relationships be correspondingly accommodated by all other
parts of the matrix without actual changes throughout the entire matrix—through
to the endpoint of the final development of form and structure. This question
alone suggests we just can't arrive at complexity of this sort in a simple
stepwise fashion. A coordinated multiple gene change would be required for
any one genetic mutation—yet multiple 'coordinated' random mutations
would be the rarer case.

Almost every
gene that has been studied in higher organisms has been found to affect
more than one organ system, a multiple effect which is known as pleiotropy. Denton (ETC) Page 149

What options are their
for a response to embryological evidence against the standard assumptions
supporting evolution theory?

Since
1980, with the rapprochement between developmental and evolutionary
biology, there has been a growing recognition that the early stages
of embryogenesis contradict Darwin's view. Rather than seeing a embryological
evidence as a threat to evolutionary theory, however, Darwinian biologists
now welcome it as a new source of support. Their reasoning goes something
like this: major evolutionary changes require major changes in development;
if similar morphologies (such as pharyngula) can
be reached by very different developmental pathways, as in the vertebrates, then early development
must be more changeable than we thought; since early development is
so changeable, then large-scale evolution must be relatively
easy to achieve. Wells (MC)
Page 60

Yet the difficulties
are hard to ignore, especially where the problems facing the evolutionists
run deep.

On turning
to the observations, however, we find striking differences in early
development (see figure 6.2 for some examples strictly within the
vertebrates). Eric Davidson (1990, 365) remarks on these differences,
calling them "anything but trivial and superficial," ... Nelson
(MC) Page 154

And again (Davidson 1994, 604):

The initial embryonic specification
strategies employed by organisms of different phylogenetic groups
actually differ from one another to a surprising extend, however.
In some embryos, specification depends on intracellular interaction
during cleavage, while in others this cannot
be so since specification occurs while the nuclei are syncytial;
some rely on invariant cell lineages, while others develop from
populations of migratory cells of no fixed of lineage; some generate
autonomously specified founder cells, while others have none; and
so forth. Nelson (MC)
Page 155

Note that there are
differences in embryos to be observed concerning the role of different groups
of cells. Some stay relatively fixed in place while others move or migrate
about to a place for their continued and fateful biological development. Embryologists
have made studies in great detail to follow each new cell division and to
track the destiny of each and every cell as it gives rise to tissues, then
organs or appendages. If there are differences in the lineages or 'cellular
pathways,' so to speak, then the avenues of development reveal a corresponding
dissimilarity. If not, then what continuity is here to speak of a common ancestry?

Recall also,
as we have just noted, that early development is strikingly diverse
in the animals. How then did these remarkable differences evolve from
a common ancestor? Nelson
(MC) Page 156

To add another voice to the discussion on
embryological recapitulation, points made by Dr. Wise restate as well as add
to what we've noted thus far:

One
evidence of macroevolution popularly heralded in the latter part of
the nineteenth century was embryological recapitulation. According
to this hypothesis, as organisms develop from a fertilized egg, they
pass through stages very similar to the evolutionary stages of their
ancestors. Each human, for example, starts as a single cell—as
all life supposedly did—then develops through a wormlike stage,
then a fishlike stage (complete with gill slits), then a froglike
staged, then a stage in which there is a tale, and finely this stage
of a human child. In this way and organism's embryology (development)
recapitulates (briefly repictures) its phylogeny (evolutionary history). Wise (CH) Page 215

Third, although developmental stages
appeared to be broadly similar to earlier evolutionary stages,
when examined closely the similarities break down. In human development,
for example, the fertilized egg is a diploid eukaryotic cell with
twenty-three chromosome pairs—not a haploid prokaryotic cell
with a single strand of DNA from which we supposedly evolved. In a
like manner, this similarity between human developmental stages and
worms and frogs breaks down very quickly upon close examination. The
so-called gill slits in human development are not gill slits, and
did the "tail" in human development is not actually a tail. These
things only bear superficial resemblance to those structures.

Fourth, in many cases development
and runs through stages in "incorrect" order for phylogeny. In sum,
embryological recapitulation suffers from too many difficulties to
be considered a viable theory. It has been rejected by a number of
evolutionary biologists and has been expunged from the textbooks over
the years. Wise
(CH) Page 216

There is a lot more
to the storyline emerging here. This in part is why we've recommended a book
for further reading and drawn comments from several other sources. And further,
as noted in the side bar above, t here are other interesting problems that
arise from a closer look at data from embryology. Again there appear to be
serious problems related to assuming that random mutations occurring during
embryo development lead to evolutionary innovations. The intricate nature
of an embryo's early development illustrates how random mutations end up with
lethal results. Further discussion of this aspect of embryology will appear
in a future feature article here within the WindowView [When
ready, a link will be added here]. And as noted above, this article
will be based on comments made by Drs. Meyer and Nelson at the Yale
Symposium held November 2000.

Added
Perspective:

What else is to be
made of embryological evidence. The various articles within the WindowView
have done more than to simply hint that more is afoot in nature than chance
events. The specificity we see in biological systems in drawing more and more
attention to the design that is inherent in these natural systems. And if the design reflects an intelligence
and is observed in more and more unique locations throughout the natural world,
then design becomes an ever larger possibility. That this has been repeatedly
ignored is insufficient as a disproof for the existence of design. Again,
evolution theory is eloquent in its simple explanations, until the complex and specific examples unveil elements of intelligent
design. One is explained by chance,
the other stands where chance events fail as an explanation. So, we will leave
you with a hint of the what comes by building the window's larger view. A
natural perspective is the norm. Opening the floor to discussing design is
a growing part of a new dialog.

From
a naturalistic perspective, development of supposedly proceeds mechanistically,
like a ball rolling down a hill. Changes in developmental pathways
are likely to produce alterations in the final outcome, and the earlier
the changes, the more drastic the alterations.

From a design perspective,
however, it is possible to regard development as an end-directed process.
If organisms are designed, which is to say produced according to a
preconceived plan, then in some sense their final form precedes their
embryonic development. Wells
(MC) Page 61

If you are new to the
Science Area feature articles within WindowView, then we respectfully ask
that you keep in mind two very different perspectives—one based on naturalism
and the other on design. And then read on to see what happens with these different
vantage points.

If you have been reviewing
the Science Area narrative, skim reading or exploring the details in the feature
articles that precede this one on embryology, then a broader picture is already
in view. It's not entirely important to declare design is wholly a valid concept or fact at this stage of the game—not needed
to get the main point concerning assumptions rooted in the work of Haeckel
and Darwin. However, based on the information above and by reading the source
material upon which this article is based, there is indeed a consistency with
the issues discussed throughout the entire Science Area. Design may be a new
term in the biological vocabulary to many of our readers, but by all appearances,
this is a term that's here to stay.

Quotations
from "Mere Creation" (MC) edited
by William A. Dembski are used by permission
of InterVarsity Press, P.O. Box 1400, Downers
Grove, IL 60515. www.ivpress.com All rights
reserved. No portion of this material may be
used without permission from InterVarsity Press.

Quotations from "The Creation Hypothesis"
(CH) edited by J. P. Moreland and "Mere Creation" (MC) edited by William
A. Dembski are used by permission of InterVarsity Press, P.O. Box 1400, Downers
Grove, IL 60515. www.ivpress.com All rights reserved. No portion of this material
may be used without permission from InterVarsity Press.

Writer / Editor: Dr. T. Peterson, Director,
WindowView.org

(090204)

For a general listing of books, visit the WindowView Book Page for: Science and Scripture .

References of Interest

Step Up To Life

Time spent looking ... through a window on life and choice ... brings the opportunity to see in a new light. The offer for you to Step Up To Life is presented on many of the web pages at WindowView. Without further explanation we offer you the steps here ... knowing that depending on what you have seen or may yet explore in the window ... these steps will be the most important of your life ...